What are the basic types of actors that can exist in a Use Case Diagram?

ANSWER

Actors can be primary or secondary actors. Primary actors initiate a use case, while secondary actors support a use case or receive something of value from the use case. While this answer might score you some points in the interview, there is another way to classify actors that is important to know and can show that you understand some of the finer points of use case diagramming.

Actors can be:

Human

Systems/Software

Hardware

Timer/Clock

Many analysts miss key actors during the use case diagramming process because they only identify human actors. Categorizing use case actors in this ways helps the analyst ensure they haven’t overlooked any critical actors within the use case diagram.

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ADDITIONAL ANSWERS / COMMENTS

Up to UML version 2.0, the Primary Secondary Classification of Actors has not been defined. Alistair Cockburn and Craig Larman have referred to them (It was said that Ivar Jacobson had defined them) but the explanation given above is not consistent with their interpretation.

Primary Actors are those TO WHOM System provides services. (Customer)

Secondary Actors are THOSE WHO HELP THE System to provide the services. (system Administrator or cash loader of ATM).

It is OK to know this distinction but nothing significant is gained applying it.

Regarding the triggering there are two views.

1 System presents the home page or the first dialog box for every use case and so it triggers every use case / sub-use case.

2 1 is true for all use cases but it is dormant or inactive. The real activation is done by an external Actor.

So, it is NOT much useful for classification or analysis.

The question should be more pointed to get the right answer.

putchavn@yahoo.com

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